6. Lunges
Lunges, when done correctly, can engage your hip flexors and allow you to stretch them out so you can prevent hip flexor strain. You are probably already familiar with how to lunge is accomplished, but if not, here is a quick tutorial.
You will stand with your knees slightly bent and one foot in front of the other. You will go forward on one foot, for example, the right foot and go down to the ground as low as you can. Then you will come back up slowly and switch legs.
Instead of switching legs, some people prefer to come back up into the starting position and then repeat the exercise of the same leg instead. Other people prefer to do alternate legs when they are doing their lunges. There is no wrong way to do them so you will have to decide for yourself.